This application claims the priority of German patent application 101 57 074.0, filed Nov. 21, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an air data measuring device and to an air data system for flight vehicles, particularly a device for measuring flight conditions at large airplane angles of incidence.
The measuring device according to the invention and the measuring system according to the invention respectively can be used in the case of flight vehicles of all types, particularly in the case of airplanes and missiles.
Conventional air data systems are operable only in a limited angle of incidence range and are arranged on the airplane such that only the lower angle of incidence range of up to approximately 30xc2x0 can be detected.
In particular, rigid air data probes arranged for example at the tip of the fuselage and based only on pressure measurements are known, and are provided also for large angles of incidence of up to 90xc2x0. However, such probes require extensive and high calibrating expenditures.
It is therefore an object of the invention to provide a suitable probe and a corresponding air data system which permits precise measurement at large angles of incidence and yaw angles, as well as high flying speeds and altitudes, with minimal equipment-related and functional costs.
These and other objects and advantages are achieved by the air data measuring device according to the invention, in which a probe carrier arranged on a structural part is rotationally symmetrical at least at a transition boundary. By means of a bearing, it is rotatably about its longitudinal axis disposed on the structural part, and its mass, is balanced about its longitudinal axis. The angle of rotation (xcfx86S) of the probe is measurable by way of a measuring sensor, on the probe. At least two strakes are arranged symmetrically to the plane of symmetry of the probe, so that the probe angle of yaw xcex2S of the probe is minimized in the case of each on-coming flow condition. For detection of differential pressures and of an absolute pressure at the probe surface, at least three pressure measuring bores are provided with differential pressure sensors assigned to the latter. Of the pressure measuring bores, the first is situated in the center, or at a radial distance from the center which is smaller than the radial distance from the center of the second pressure measuring bore, while the radial distance of the third bore from the center is equal to or larger than the radial distance of the second pressure measuring bore from the center. One of the pressure measuring bores is situated in the plane of symmetry of the probe and the two other pressure measuring bores are asymmetrical to one another with respect to the plane of symmetry, in order to determine by means of calibrating functions, the air data of the undisturbed flow and check the alignment of the probe.
According to the invention, a symmetrical probe in the shape of a radome tip, which is rotatable about the longitudinal axis of the airplane radome and which has at least one pair of strakes arranged on its circumference, is used as the air data probe. As a result of its aerodynamic influence, the pair of strakes causes a rotating position of the rotatable probe on the airplane. In a sideslip state, a torsion angle xcfx86S is thereby created about the radome axis relative to the plane of symmetry of the airplane. By means of the torsion angle xcfx86S, the probe is situated in a position in which by way of corresponding pressure bores on its surface, a slip-free measuring of its angle of incidence xcex1S can take place.
According to the invention, on the surface of a rotatable probe, which preferably forms the top of a radome, at least three pressure measuring bores are provided. By means of these bores, for each angle of incidence xcex1S of the probe, a differential pressure ratio   R  =      (                            p          2                -                  p          1                                      p          1                -                  p          3                      )  
can be determined which is independent of the flight altitude and of the flying speed. By way of calibrations carried out, for example, in a wind tunnel and the determined calibrating function R=R(xcex1S), the inverted function xcex1S=xcex1S (R) is implemented in the air data measuring device or the air data system, such that the angle of incidence of the probe xcex1S can be determined. From the measured actual torsion angle of the probe xcfx86S about the longitudinal axis of the radome and the determined angle of incidence of the probe xcex1S, by means of the measured differential pressures and the calibration, an angle of incidence and of yaw xcex1F and xcex2F respectively can be determined at which the airplane is flying. The detection of the flight altitude and flying speed takes place by means of an absolute-pressure and differential-pressure sensor. To determine the actual absolute static pressure of the undisturbed flow (by means of which the flight altitude is determined), the influence of the flying speed is eliminated by means of the respective differential pressure.
The described system is preferably provided as a supplement to a conventional system, specifically for measuring large angles of incidence. Furthermore, when the air data system according to the invention is operated in combination with a conventional air data system, safety demands can be met in an improved manner by the availability of redundant measurements. However, the system can also be utilized as a sole pressure measuring system in the relevant angle of incidence range.
The invention has the following advantages:
The arrangement of the probe is situated in the fuselage tip area (or alternatively on a structural part projecting into the flow), so that an undisturbed flow against the probe as well as its radar compatibility is provided. In this case the radome axis or the axis of the structural part can be used as the weathercock axis when, at least in its forward area, the probe forms a rotationally symmetrical body;
outlays for establishing and implementing the calibrating functions are relatively low because of the aerodynamic alignment of the probe in the flow, since a slip-free measurement of the angle of incidence of the probe takes place and the aerodynamic calibration of the angle of yaw influence is eliminated;
the calibration of the angle of incidence of the probe takes place by a differential pressure ratio which is independent of the altitude and speed, and is determined on the basis of the measurement of at least two differential pressures by means of at least three pressure measuring bores;
an increase of the measuring precision of the angle of incidence is permitted in a simple manner by using corresponding differential pressure sensors with a reduced pressure range for the relevant flight range and corresponding bypass lines, without changing the system concept;
the determination of the flight altitude takes place by measuring the absolute pressure at a measuring bore as well as of a differential pressure between two pressure measuring bores at the probe surface, whereby a speed independence of the measuring parameter, thus of the static pressure of the undisturbed oncoming flow, is achieved.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.